Heating System For Heating A Heat Shrink Component, Heat Shrink Component, And Method Of Assembling A Heat Shrink Component

ABSTRACT

A heating system for heating a heat shrink layer of a heat shrink component during a heat shrink process includes a heating unit arranged in thermal contact with at least a part of the heat shrink layer and heating the heat shrink layer to a heat shrink temperature. The heating unit has a first heating zone and a second heating zone. The first heating zone has a different heating energy than the second heating zone for a period of time of the heat shrink process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2018/068164, filed on Jul. 5, 2018, which claims priority under 35U.S.C. § 119 to European Patent Application No. 17181399.1, filed onJul. 14, 2017.

FIELD OF THE INVENTION

The present invention relates to a heating system and, moreparticularly, to a heating system for heating a heat shrink component.

BACKGROUND

Heat shrink components are articles made from material which shrinksfrom an expanded state into a shrunk state with much smaller dimensionsby applying a sufficient amount of heat. Heat shrink components arewidely spread as joint sleeves or other cable accessories.

A heat-recoverable article (an independently dimensionally heat-unstablearticle) can function as a heat shrink layer. In general, such anarticle is made of a material capable of having the property of elasticor plastic memory imparted thereto which is heated to a certaintemperature and distorted under pressure to a configuration differentfrom its normal configuration and then cooled while kept under pressure.If the article is made of a material which is wholly or partlycrystalline, is at least partly cross-linked in the amorphous areas, andis distorted at a temperature at or above the crystalline melting pointof the material, the article will have elastic memory. An article withelastic memory will not recover towards its original configuration untilit is again heated at least to its crystalline melting temperature. Ifthe article is made of a non-crystalline material, it is heated to atemperature at which the article can be distorted by pressure, and thedistorted article then has the property of plastic memory. Examples ofheat-recoverable materials are found in U.S. Pat. Nos. 2,027,962 and3,086,242. Of course the heat shrink layer can be fabricated from anysuitable material, as this is known to a person skilled in the art.Moreover, also multilayer arrangements can additionally comprise elasticand/or electrically semi-conductive and conductive layers.

In order to install heat shrink products for low-voltage (“LV”),medium-voltage (“MV”), and high-voltage (“HV”) applications, typicallyopen flames, such as gas torches, are used. More rarely, also hot airguns with several kilo watt (“kW”) of power are employed. Hot air guns,however, are limited to thin walled products, like LV sleeves and moldedparts with a low wall thickness in the range of 1 to 4 mm. For instancefor electronic applications, where sleeves typically have wallthicknesses below 1 mm in the expanded state, hot air guns or tunnelheaters with ceramic radiation features are commonly used.

From the perspective of safety, the use of open flames isdisadvantageous. Furthermore, it is desired to reduce the amount ofenergy needed for installing products. In some cases it is also desiredto reduce the amount of heat generated during installation.Consequently, it is desirable to use other energy sources than openflames, preferably electrical energy.

It is known to shrink heat shrinking products by adding at least onelayer to the product that transforms electrical energy into heat. FromDE 1941327 A1, an electrically conductive heat-recoverable article isknown which recovers by passing an electrical current through thearticle to raise it to its recovery temperature. The conductive article,e.g. a tubular sleeve, is placed in good heat-transfer relationship toan electrically non-conductive heat recoverable member, e.g. a tubularsleeve, so as to act as heater for this non-conductive member, the twomembers recovering substantially simultaneously. The conductive materialof the sleeve is carbon-black filled cross-linked polyethylene which ismade heat-recoverable. Other cross-linked polymers, non-crystallinepolymers such as polyurethane and ionomers, as well as elastomers suchas silicone rubber are disclosed. A conductive sleeve is surrounded bytwo insulating sleeves, or a slit conductive sleeve surrounds aheat-recoverable non-conductive sleeve and is peeled away after thenon-conductive sleeve is fully recovered. Electrical connections to theconductive sleeves are established via alligator clips or otherconventional clamps or electrodes.

However, these known arrangements suffer from the disadvantage that thetime for performing the installation is usually greater than 15 minutesand therefore too long to be cost effective.

Furthermore, it is known to provide heating systems with fluid pipes inorder to prevent fluid conducted by the pipes from freezing. Thesedefrosting systems, however, allow only maximum temperatures of about 60to 80° C. and are therefore not applicable for shrinking heat shrinkproducts which require temperatures above 120° C.

Outside the field of energy technology, it is known to use electricalheating for jointing pipes using thermoplastic coupling parts. As forinstance disclosed in European patents EP 1190839 B1 and EP 0798099 B1,a molded part with embedded wires is positioned over the end portions ofthe two pipes to be joined. An electronic drive system linked to a powersource then generates sufficient heat to melt the ends of the pipeswhich then are welded with each other and/or the molded part. For thisfield of application, the pipes essentially do not change their originaldiameter and each joint component is only used for one particulardiameter of pipes. When applying such a system to a heat shrinkcomponent which usually undergoes a diameter reduction of around 10% to75% of the expanded diameter during the heat shrink process, the moldedpart would lose mechanical contact to the heat shrink product.

Finally, there exist multiple heating systems in the art which are basedon resistance wires. These wires are made from special metal alloys thathave resistance values which are about 10 to 100 times higher than thoseof copper or aluminum. The disadvantage of using resistance heatingwires can be seen in the fact that these standard resistance heatingwires have a high specific resistance and therefore provide a highdensity of dissipated heat energy, so that for reaching a temperature of120° C. and higher by applying a voltage of about 24 V, only a shortlength of wire is needed. This rather short wire length causes severeproblems to properly distribute the heat over the entire surface andvolume of a typical heat shrink product such as an MV joint body. Inaddition, the costs of heating wires are much higher than of forinstance copper wire.

Moreover, it was found that when using wires for heating up the heatshrink material within the allowed time (e.g. 10 min for a thickerwalled MV joint body), they may have temperatures of 150° C. or higher,sometimes even to 450° C. In these cases, the direct contact of the hotwires may cause the heat shrink material to fail due to materialdegradation. For instance, splitting of a heat shrink sleeve or thedestruction of thin superficial conductive layers on the heat shrinksleeve may occur, resulting in electrical failure once the cableaccessory is energized. Thus, it has to be ensured that heating wirescan be operated to generate high temperatures, at the same time avoidingharming the heat shrink component.

Apart from avoiding temperature peaks and local overheating at theelectrically conductive leads, a fast and even energy input towards theheat shrink material is of utmost significance for achieving the shortshrinking durations that are required to be market competitive. Inparticular, a fast and even shrinkage of an essentially tubular heatshrink component around its entire circumference has to be ensured. Heatshrink cable accessories change their diameter by large degrees in thecourse of their installation process in order to conform to variouscable diameters. These range taking properties strongly influence theheating system. An even shrinkage is important for cable accessories inorder to close axial interfaces of joints and terminations. If the heatshrink product is a sleeve that has the purpose of sealing against theenvironment, an even shrinking is needed for instance to melt a hot meltarranged on the inside of the sleeve and to soften the sleeve itself inorder to allow for a proper sealing.

However, it was found that a uniform heating along an axial direction isnot always an optimal heating scheme because it is often desired thatthe shrinking process starts in one particular zone and proceeds intoone or more axial directions towards peripheral ends of the heat shrinkproduct until the complete heat shrink product has reached the finalshrunk state. By such a gradual progression of the shrinking processalong an axial direction, undesired gas inclusions between the heatshrink component and the object to be covered can be avoided. When usingopen flames, a human operator performing the heat shrinking processachieves such a progressive shrinking by adequately moving a torch alongthe heat shrink component.

SUMMARY

A heating system for heating a heat shrink layer of a heat shrinkcomponent during a heat shrink process includes a heating unit arrangedin thermal contact with at least a part of the heat shrink layer andheating the heat shrink layer to a heat shrink temperature. The heatingunit has a first heating zone and a second heating zone. The firstheating zone has a different heating energy than the second heating zonefor a period of time of the heat shrink process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying Figures, of which:

FIG. 1 is a schematic diagram of a heat shrinking process of a heatshrinkable joint sleeve;

FIG. 2 is a schematic diagram of a heating unit according to anembodiment;

FIG. 3 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 4 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 5 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 6 is a sectional end view of a plurality of electrically conductiveleads;

FIG. 7 is a sectional end view of a plurality of electrically conductiveleads;

FIG. 8 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 9 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 10 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 11 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 12 is a detail of a portion of FIG. 11;

FIG. 13 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 14 is a sectional schematic diagram of a heating unit according toanother embodiment prior to assembly;

FIG. 15 is a sectional schematic diagram of the heating unit of FIG. 14fully assembled;

FIG. 16 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 17 is a sectional schematic diagram of a heating unit according toanother embodiment;

FIG. 18 is a schematic diagram of a heat spreading mechanism of theheating unit of FIG. 9;

FIG. 19 is a schematic diagram of a heat spreading mechanism of theheating unit of FIG. 11;

FIG. 20 is a schematic diagram of a heat spreading mechanism of aheating unit according to another embodiment;

FIG. 21 is a schematic diagram of a heat spreading mechanism of aheating unit according to another embodiment;

FIG. 22 is a schematic diagram of a heat spreading mechanism of aheating unit according to another embodiment;

FIG. 23 is a schematic diagram of a heat spreading mechanism of aheating unit according to another embodiment;

FIG. 24 is a schematic diagram of a heat spreading mechanism of aheating unit according to another embodiment;

FIG. 25 is a sectional schematic diagram of a heat shrink componentaccording to an embodiment;

FIG. 26 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment;

FIG. 27 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment;

FIG. 28 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment;

FIG. 29 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment;

FIG. 30 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment.

FIG. 31 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 32 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 33 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 34 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 35 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 36 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 37 is a schematic diagram of a heating unit according to anotherembodiment;

FIG. 38 is a schematic diagram of a heat shrink component according toanother embodiment;

FIG. 39 is a schematic diagram of a heat shrink component according toanother embodiment;

FIG. 40 is a schematic diagram of a heat shrink component according toanother embodiment;

FIG. 41 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment;

FIG. 42 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment; and

FIG. 43 is a sectional schematic diagram of a heat shrink componentaccording to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Exemplary embodiments of the present disclosure will be describedhereinafter in detail with reference to the attached drawings, whereinlike reference numerals refer to like elements. The present disclosuremay, however, be embodied in many different forms and should not beconstrued as being limited to the embodiments set forth herein; rather,these embodiments are provided so that the present disclosure willconvey the concept of the disclosure to those skilled in the art.Furthermore, several aspects of the embodiments may form—individually orin different combinations—solutions according to the present invention.The following described embodiments thus can be considered either aloneor in an arbitrary combination thereof.

The term “high-voltage” as used in the following is intended to relateto voltages above approximately 1 kV. In particular, the termhigh-voltage is intended to comprise the usual nominal voltage ranges ofpower transmission, namely medium voltage, MV, (about 3 kV to about 72kV), high-voltage, HV, (about 72 kV to about 245 kV), and also extrahigh-voltage (up to presently about 500 kV). Of course also highervoltages may be considered in the future. These voltages may be directcurrent (DC) or alternating current (AC) voltages. In the following, theterm “high-voltage cable” is intended to signify a cable that issuitable for carrying electric current of more than about 1 A at avoltage above approximately 1 kV. Accordingly, the term “high-voltageaccessory” is intended to signify a device that is suitable forinterconnecting high-voltage facilities and/or high-voltage cables. Inparticular, a high-voltage accessory may either be an end termination ora cable joint. The present invention is also applicable to the so-called“low-voltage”, LV, range that relates to voltages below 1 kV. Theprinciples of the present invention may further be applied to heatshrink products used for electronic applications.

When referring to a “layer” in the following, it is not intended to meanthat the object underneath has to be covered completely by the layer.

A heat shrinking process of heat shrinkable joint sleeve 100A, 100B isshown in FIG. 1. The heat shrink sleeve is in the expanded state 100Awhere it has first dimensions. The heat shrink sleeve in the expandedstate 100A has an inner diameter 102A which is larger than the outerdiameter of a component to be covered and a wall thickness 104A that isthinner than in the finally mounted state. By applying heat, the heatshrink sleeve is transformed from the expanded state 100A into a heatshrink sleeve in the shrunk state 100B (indicated by the arrow). Inorder to be shrunk under the influence of heat, the sleeve 100 has aheat shrink layer heat.

A heat-recoverable article (an independently dimensionally heat-unstablearticle) is used as the heat shrink layer 108. In various embodiments,the heat shrink layer 108 can be fabricated from any suitable material.In other embodiments, the multilayer arrangements additionally compriseelastic layers. Heat shrink layers 108 and/or elastic layers maycomprise electrically insulating and/or electrically semi-conductiveand/or conductive layers or components.

As shown in FIG. 1, the shrunk sleeve 100B has an inner diameter 102Bthat fits tightly over the covered component and a larger wall thickness104B as compared to the expanded state 100A. The heat shrink processleads to a reduction of diameter 102B of up to 75% of the diameter 102Ain the expanded state 100A. The principles according to the presentinvention can be applied to straight tube shaped sleeves 100 as well asto differently shaped covers for branch joints, elbows, bends, and thelike. The component onto which the sleeve 100 is shrunk may becylindrical or it may have regions with a cross-section that ispolygonal and/or that is varying along the longitudinal axis of thecomponent.

The heat shrinking step is performed by applying electrical energy viaelectrically conductive leads 106 with an electrical conductivity ofmore than 1·10⁷ S/m and, in an embodiment more than 3·10⁷ S/m, whichcomprise copper and/or aluminum. In an embodiment, the electricallyconductive lead 106 comprises copper and has an electrical conductivitygreater than 4·10⁷ S/m.

FIGS. 2-5 illustrate examples of how the electrically conductive leads106 that form a heating unit 120 can be arranged on a heat shrinkproduct. The leads 106 may be positioned with direct contact to a heatshrink layer or may be positioned on a layer of non-shrink material,such as an elastomeric layer or a thermoplastic layer. Terminals are ledto the outside for connecting a power source, such as a batterysupplying a DC voltage of, for example, 24 V. In an embodiment, thepower source provides a DC voltage below 60 V or an AC voltage of 25 Vroot mean squared (“RMS”).

A length of the electrically conductive lead 106 is determined by adiameter and a resistance value that is to be reached and amounts toaround 1 to 15 m when choosing a diameter in a range of 0.1 mm to 0.4mm. The resulting overall resistance of such heating units 120 may forinstance be in a range of 0.3Ω to 6.0Ω at 23° C.

In the embodiment shown in FIG. 2, a plurality of elongated wiresections 112 are arranged in parallel to a longitudinal axis 110 of theheat shrink sleeve 100. The individual wire sections 112 may be seriallyinterconnected in the fashion of a meandering structure to form onecontinuous electrical lead 106. Additionally, some of the longitudinalsections 112 may be interconnected to form an elongated closed loop, aplurality of those loops being interconnected in parallel. The sections112 may either be arranged on an outer surface or on an inner surface ofthe heat shrink sleeve 100. The sections 112 may also be covered byfurther layers. The sections 112 may also be arranged in differentplanes with respect to the center line 110.

Arranging the wire sections 112 in parallel to the longitudinal axis 110of the heat shrink sleeve 100 is also advantageous from anelectro-physical point of view because undesired coil structures can beavoided. If necessary, the loops of wire interconnecting the wiresections 112 for providing a closed path for the current may be arrangedat the periphery of the sleeve 100 in a way that they can be cut offafter the shrinking process is completed, leaving in place only thelongitudinal wire sections.

The embodiment shown in FIG. 2 having the longitudinal wire sections 112has the advantage that, upon shrinking of the heat shrink layer 108, thewire sections 112 become arranged closer to each other, but are notsignificantly deformed or dislocated. If the covered component has apolygonal cross-section and/or has dimensions that vary along thelongitudinal axis, the wire sections 112 conform to this outersilhouette to some extent. Still, no sharp edges or disruptions duringthe heat shrinking process can occur. This means that separations orareas of increased resistance due to strong deformation of the wires areless likely.

In an embodiment shown in FIG. 3, a plurality of ring-shaped wires 114are arranged on the sleeve 100 to form the electrically conductive lead106. These ring-shaped wires 114 are arranged equidistantly along thelongitudinal axis 110 and are essentially perpendicular to thelongitudinal axis 110. In other embodiments, the ring-shaped wires 114can also be arranged with varying distances between each other.Moreover, when using an elliptical shape instead of a circular geometry,the rings 114 can also be arranged to include an angle other than 90°with the longitudinal axis 110. The rings 114 may electrically beconnected in series and/or in parallel. For a serial connection, therings 114 may not be entirely closed around the circumference of theheat shrink sleeve 100.

In an embodiment shown in FIG. 4, one continuous electrically conductivelead 106 is wound in a helical configuration around the heat shrinklayer 108. This configuration is particularly easy to assemble.

The above-described arrangements according to FIGS. 2-4 can also becombined with each other as is exemplarily depicted in FIG. 5. In theembodiment of FIG. 5, one layer of longitudinal sections 112 is combinedwith one layer of ring-shaped wires 114, wherein it is arbitrary whichlayer is the top layer and which one the bottom layer. In anotherembodiment, more than two layers can be combined to form a heating unit.Electrically, these layers may either be connected in parallel orserially. Advantageously, the wires 112, 114 in the different layers areto be electrically insulated against wires 112, 114 of another layer.This may be achieved by using wires 112, 114 that are individuallycovered with an electrical insulation and/or by arranging an insulatingmaterial between adjacent layers of wire 112, 114.

Several examples of electrically conductive leads 106 are shown in FIG.6. An electrical resistance suitable for generating temperatures around120° C. and up to 450° C. from safety voltages (e. g. 24 V DC) can alsobe realized with a highly conductive material when reducing thecross-sectional area and/or enhancing the length accordingly. Thecross-section of the wires 106 may be circular (electrically conductivelead 106A), elliptic (electrically conductive lead 106B), or polygonal(electrically conductive lead 106C). Furthermore, the electricallyconductive lead may also be formed by a thin film 116. It should benoted that the drawings are not exactly to scale throughout the Figures;in particular, the thickness of the electrically conductive film 116 isexaggerated.

The electrically conductive film 116 shown in FIG. 6 may, for instance,be formed from a metallization layer that is etched by aphotolithography process. Alternatively, also screen printing or otherprinting techniques can be used for depositing the electricallyconductive film 116 on the heat shrink layer, or on an additional layer,i. e. a thermoplastic film.

The electrical resistance of the electrically conductive lead 106 willnow be described in greater detail with reference to FIG. 7. FIG. 7shows arrangements that have the same electrical resistance, leading tothe same heating effect when powered with the same voltage. Inparticular, the cross section of a standard resistance heating wire 118is compared to a copper wire 106 or an electrically conductive copperfilm 116. When assuming that the copper wire 106A and the electricallyconductive film 116 have only 1% of the specific resistance of theresistance wire 118, they need to have a cross sectional area of only 1%of the cross-sectional area of the resistance wire 118 in order toprovide the same overall resistance for a piece of lead having the samelength. Alternatively, a copper wire 106A having 20% of thecross-sectional area of the resistance wire 118 has the same resistanceas the resistance wire 118, if the copper wire 106A has 5 times thelength of the resistance wire 118.

Due to economic and reliability considerations, the number and diameterof the heating wires 106 needs to be within certain limits. If the wires106 have very small diameters, their numbers and/or length need to bereduced. Otherwise, the resistance increases too much and voltages of 24V or below cannot generate a sufficiently high current to heat up thewires 106 to temperatures of at least 110° C. On the other hand, if thewires 106 have too large cross-sections, their resistance may become toolow. Then the length has to be increased, in order to increase theresistance. Otherwise, the wires 106 would not be heated upsufficiently. Thereby costs are increased. A further option is to use(at least in particular areas of the heat shrink component) two or moreelectrical circuits of heating wires which are connected in parallel.The electrical current then splits up according to the relativeresistance of the circuits. This allows choosing wires 106 with smallercross-sections, while achieving the same resulting resistance as with alarger size wire. In other words, two wires are connected in paralleland have each half of the cross-section compared to a benchmark wire.This principle, however, gets to some limits regarding economicconsiderations, such as the cost of fine wires relative to standardwires, and regarding reliability issues, because handling of extremelyfine wires with diameters of less than 100 μm is cumbersome.

In addition to only using the electrically conductive lead 106 as theheating unit 120, additional heating elements 122 can also be provided,as shown in FIG. 8. In an embodiment, the electrically conductive lead106 generates only negligible amounts of heat. The main part of the heatis generated by the additional heating elements 122. The heatingelements 122 may for instance be formed from semiconductor heatingelements. The electrically conductive leads 106 that are interconnectingthe heating elements 122 may either be formed as sections of wire, or byfilm-shaped electrically conductive leads. Any of the diametersexplained with reference to FIG. 6 can be employed. In an embodiment,the semiconductor heating elements 122 may have a positive temperaturecoefficient (PTC) so that an inherent overheating protection isprovided.

In an embodiment, sensors may be added to the heat shrink component.These sensors can be configured to monitor and/or drive the heating andshrinking process and give feedback for instance to the cable jointerand/or the electric drive system e. g. whether the installation has beenfinished successfully. In particular, when realizing the heating unit120 as a thin film arrangement 116, the sensors and the heating unit 120can be formed on a common flexible substrate that is attached to thesleeve.

For all of the above illustrated arrangements of electrically conductiveleads 106, the present invention proposes spreading the heat generatedby the electrically conductive leads 106 around the circumference of theheat shrink layer 108. A heat spreading layer 124, shown in FIG. 9,allows for a more even and faster energy input into the heat shrinklayer 108. Furthermore, if the heat spreading layer 124 is arrangedbetween the electrically conductive leads or heating wires 106 and theheat shrink layer 108, it also avoids heat spikes and potential damageto the heat shrink layer 108.

As shown in FIG. 9, the heating unit 120 comprises (at least inparticular areas of the heat shrink component 100) a heat spreadinglayer 124. The heat spreading layer 124 may, for instance, be formedfrom metal, such as copper or aluminum, or from a polymer which isprovided with an enhanced thermal conductivity by adding suitablefillers.

The heat spreading layer 124 may also comprise alternatively oradditionally one or more metallic layers. The electrically conductiveleads or heating wires 106 should not come into direct contact with eachother or an electrically conductive surface in order to avoid localshort circuits that would influence the overall resistance of the entireheating system. Consequently, in case a metallic heat spreading layer124 is provided in contact with the conductive leads 106, the individualleads 106 may for instance be covered with a thin electricallyinsulating layer. In an exemplary arrangement, the heating wires 106 maybe attached to a heat shrink sleeve of a joint body in an axialdirection (as shown in FIG. 2), have a diameter of less than 400 μm andbe circumferentially spaced from each other by about 5 mm to 30 mm. Withthis arrangement, a single film of copper or aluminum as the heatspreading layer 124 having a thickness of less than 400 μm is sufficientto remarkably contribute to an even shrinkage around the circumferenceof the joint body.

In another embodiment, shown in FIG. 10, a second heat spreading layer124′ is arranged to cover the electrically conductive leads 106.

In another embodiment shown in FIG. 11, the electrically conductiveleads 106 may at least partly be embedded within an embedding material126. The embedding material 126 may for instance comprise an adhesive, ahot melt material, mastic, or a lubricant, or any other suitablematerial which at least partly encloses the electrically conductive lead106 and improves the heat transfer towards the heat spreading layer 124,as will be explained in more detail with reference to FIGS. 18-24.Additional fillers in the above mentioned materials may improve theeffect.

The electrically conductive leads 106, as shown in FIG. 12, may comprisea metal lead 156 forming a core which is covered by an electricallyinsulating layer 154. This arrangement is advantageous if the leads 106may come into direct contact with a metal layer forming the uppersurface of the heat spreading layer 124.

In another embodiment, shown in FIG. 13, the electrically conductiveleads 106 are completely surrounded by an embedding material 126. Acover layer 128 is arranged on top of the embedding material 126. Asshown in FIG. 13, the heat spreading layer 124 may be formed from anelectrically insulating plastic layer 130, and the cover layer 128 isformed from a metal layer 132. Due to the presence of an electricallyinsulating embedding material 126, the wires 106 do not necessarily haveto be coated with an electrically insulating layer, but can be leftbare.

A heating unit 120 according to another embodiment, as shown in FIGS. 14and 15, allows for the heating wires 106 to avoid having an insulationcoating. According to this embodiment, the wires 106 are first attachedto a plastic film 130. From the side opposing to the wires 106, a heatspreading metal layer 132 is attached as indicated by the arrow 134.FIG. 15 shows the finally assembled heating unit 120. The heat spreadinglayer 124 is therefore formed as a double layer comprising at least onemetal layer 132 and at least one electrically insulating plastic layer130.

In an embodiment, the plastic layer 130 is a thermally insulating layer.Meshes or films with cutouts can be used as thermally insulating layers.In another embodiment, a mesh formed from a non-organic fabric can beused as a thermally insulating layer.

In another embodiment shown in FIG. 16, the metal layer 132 and theplastic layer 130 may both be covered with an adhesive that constitutesan embedding layer 126. The electrically conductive leads 106 are thensandwiched between these two films as indicated by the mountingdirections 134 and 136. This embodiment has the advantage that theheating unit 120 can easily be handled. It has to be noted, thataccording to the present invention, the plastic layer 130 and/or themetal film 132 may function as a heat spreading layer 124. It may befreely chosen whether either the plastic layer 130 or the metal film 132are arranged between the electrically conductive leads 106 and the heatshrink layer.

In another embodiment shown in FIG. 17, more than one heating unit 120A,120B is stacked on top of each other. The heat spreading layer 124A,124B of each may be formed from metal or plastic films. In order toavoid uncontrolled short circuits, the electrically conductive leads 106may be coated with an electrically insulating layer if metal films areused.

With reference to FIGS. 18-24, the heat spreading according to thepresent invention will be explained in more detail for variousembodiments of the heat shrink sleeve or component 100.

FIG. 18 shows a first embodiment, where a heating wire 106 is arrangedon a heat shrink layer 108, for instance a heat shrink sleeve, with anadditional plastic heat spreading layer 124. As indicated by the arrows138, the heat flow is deviated in a way that the heat shrink layer 108does not experience the same temperature peaks as it would experience ifin direct contact with the wire 106. Accordingly, damages by excessiveheat can be avoided at the heat shrink layer 108.

When additionally providing a layer of an embedding material 126, asshown in FIG. 19, more heat arrives at the heat shrink layer 108 and theheat is more evenly distributed. The electrically conductive leads 106do not have to be electrically insulated, if the embedding material 126and the heat spreading layer 124 are electrically insulating. In anembodiment, however, an insulation is provided for reliability reasons.

With respect to the embodiments explained above it was always assumedthat the heat spreading layer 124 is a continuous layer which covers alarger part of the heat shrink layer 108. However, as shown in FIG. 20,the heat spreading material 124 may also only be provided close to theelectrically conductive leads 106. The heat spreading material 124 isformed by traces of metal film 132 directly underlying the electricallyconductive wires 106. In an embodiment, an adhesive forms the embeddingmaterial 126 which at least partly surrounds the wires 106 andfacilitates handling during the manufacturing process.

As can be seen from a comparison with FIG. 19 where a plastic layer 130is used, the arrangement according to FIG. 20 achieves almost the samedegree of heat spreading, and in particular avoids spikes of hightemperature at the heat shrink layer 108 to about the same degree. Ifthe heat spreading layer is positioned only locally as shown in FIG. 20,then its thickness, in an embodiment, is below 1 mm.

FIG. 21, on the other hand, shows an arrangement with a continuous metalfilm 132 forming the heat spreading layer 124. An embedding material 126at least partly encompasses the electrically conductive leads 106. Asschematically indicated by the arrows 138, the heat flow is distributedin a direction across to the thickness of the metal layer 132 within theplane of the metal layer 132 due to the high thermal conductivity of thematerial. Moreover, the heat flow is deviated in a way that the heatshrink layer 108 does not experience the same temperature peaks as itwould experience if in direct contact with the wire 106. Accordingly,damages by excessive heat can be avoided at the heat shrink layer 108.By additionally providing a layer of an embedding material 126, moreheat which is evenly distributed arrives at the heat shrink layer 108.The electrically conductive leads 106 do not have to be electricallyinsulated, if the embedding material 126 is electrically insulating.

Of course, one or more layers with higher and lower thermal conductivitymay also be arranged in an alternating manner to form a multilayer heatspreading layer 124, as shown in FIG. 22. According to this example, aheat spreading layer with a high thermal conductivity, for instance ametal layer 132, is arranged on the heat shrink layer 108. The metallayer 132 is covered by a layer with a lower thermal conductivity, forinstance a plastic layer 130. The electrically conductive leads 106 arearranged on a second metal layer 132 which is deposited on top of theplastic layer 130. The electrically conductive leads 106 are embedded atleast partially within an embedding material 126. As indicated by thearrow 138, the heat flow is strongly spread by the metal layers 132within the respective plane of the layer. On its way from the wires 106to the heat shrink layer 108, the heat is spread quite uniformly so asto provide an even energy input around the circumference of the heatshrink component 100 and to avoid any destructive temperature peaks atthe heat shrink layer 108. With this arrangement and also with thearrangements explained referring to the other Figures, the heatspreading layer 124 permits running the heating wires 106 at much highertemperatures, ensuring an accelerated shrinking process taking placemore uniformly across the entire product.

A similar pattern of the heat distribution can be reached by forming theheating unit 120 from a flexible foil 130 with a printed pattern ofelectrically conductive film traces 116. The flexible foil 130 may forinstance be a polymeric carrier film fabricated from polyimide (PI),comprising copper layers that form the electrically conductive traces116, as shown in FIG. 23. Due to the fact that the electricallyconductive film traces 116 are in contact with its substrate not onlyalong a comparatively small surface area as this is the case with wireshaving for instance circular cross-sections, the heat is alreadydistributed over a larger area compared to a heating wire 106. Moreover,the PI foil 130 further spreads the generated heat as indicated by theheat flow arrows 138. Of course, an additional cover layer, alsofabricated from the same material as the foil 130, may also be added. Anadditional metal layer arranged between the PI foil 130 and the heatshrink layer 108 (not shown in the Figure) increases heat transfer. Sucha metal layer may also support to have only smaller pieces of such aheating system to be arranged on the heat shrink layer 108, thusreducing the costs in some cases. As shown in the embodiment of FIG. 24,the electrically conductive film traces 116 may also be covered by anembedding material 126.

There are commercially available plastic films with different layerthickness of copper (e. g. between 5 μm and 25 μm). These dimensions ofcourse lead to different widths of the conductive films 116, thuscovering the circumference to different percentages. In order to createthe same cross-section of the film as the copper wires used according tothe present invention (e. g. diameter: 0.22 mm, cross-section: 0.038mm²), the width of the films would be 7.6 mm for a thickness of 5 μm,4.2 mm for a thickness of 9 μm, and 1.5 mm for a thickness of 25 μm.

An intimate contact between the heating unit 120 and the heat shrinklayer 108 is needed for an optimal heat transfer to the heat shrinklayer 108. FIG. 25 shows an embodiment where the heating unit 120 isfirmly bonded to the heat shrink layer 108 at an interface 140. Theheating unit 120 shown in FIG. 25 is structured as shown in FIG. 13exemplarily. It is clear for a person skilled in the art, however, thatany of the other heating units according to the present invention mayalso be bonded to the surface of the heat shrink layer 108. Unless anadhesive is used for bonding the heating unit 120 to the heat shrinklayer 108, the layer of the heating unit 120 which is part of theinterface 140 (or at least a surface layer) is a plastic material thatcan be chemically bound to the surface of the heat shrink layer 108.

In another embodiment, as shown in FIG. 26, one or more additionalcompressing layers 142 may be provided for pressing the heating unit 120towards the heat shrink layer 108. Optimally, the compressing layer 142keeps the heating unit 120 in close contact to the heat shrink layer 108during the complete heat shrink procedure. The compressing layer 142exerts a mechanical force directed toward a center of the heat shrinkcomponent 100, so that the heating unit always remains in close contactwith the heat shrink layer while the diameter of the heat shrink layerdiminishes. However, some degree of delamination and therefore loss ofthe intimate contact can be tolerated and still allows a reasonableshrinking performance because the heating wires 106 also generate anoticeable amount of heating radiation. It is also important to transfera high amount of heat energy into the heat shrink layer 108 until itstarts to contract. After that, a relatively small amount of heat is tobe transferred.

As shown in FIG. 26, the compressing layer 142 may comprise a secondheat shrink layer 144 and/or a pre-stretched elastomeric layer 146.Additionally, or alternatively, as shown in FIG. 27, the compressingelement 142 may comprise a spring 148 or a spring system comprising aplurality of springs for pressing the heating unit 120 onto the heatshrink layer 108. The second heat shrink layer 144 and the pre-stretchedelastomeric layer 146 may be formed as more than one short ring.

FIGS. 28-30 show examples of how the electrically conductive lead 106can be brought into tight, albeit heat spreading contact with the heatshrink layer 108.

Firstly, as shown in FIG. 28, the electrically conductive lead 106 maybe received in accordingly formed recesses 150 of the heat shrink layer108, thereby establishing a form fit. Moreover, the electricallyconductive leads 106 can be embedded in an embedding material (not shownin this Figure). A heat spreading layer (not shown in the Figure) may beadded to encompass the arrangement.

In case that the electrically conductive lead is formed by anelectrically conductive film 116, same can be attached to the heatshrink layer 108 directly or via an electrically insulating film 130, asshown in FIG. 29. For instance, a thin, structured metal film 116 can bebonded to the surface, or the conductors 116 are printed onto thesurface of the heat shrink layer 108. Alternatively, as this is knownfor printed circuit board (PCB) fabrication, the surface of the heatshrink layer 108 may also be coated with a metal layer which is thenpatterned by means of an etching step.

Furthermore, as shown in FIG. 30, the electrically conductive leads 106may also be embedded within an embedding material and/or additional heatshrink layer 152 that is in tight contact with the heat shrink layer108. The embedding step may for instance be performed by co-extrusion.

With any of the embodiments explained above, air pockets have to beavoided because the air expands from room temperature to 120° C. andabove quickly, resulting in air bubbles that are large enough to hindera sufficient heat spreading and/or generate unwanted deformations of theheat shrink component 100. Thus, the heat shrink component 100 may bedamaged unless the presence of air bubbles is avoided to a sufficientextent.

The present invention provides—in combination with any one of the abovedescribed arrangements—a heating system that avoids entrapment of airbetween the heat shrink layer 108 and any object that is to be coveredby the heat shrink component 100. According to the present invention,the term “heating system” is intended to signify an arrangementcomprising at least one heating unit 120 that can be attached to a heatshrink layer 108 and optionally one or more heat spreading layers 124that may have one or more covering layers 128, and may have one or morethermally insulating layers 130, and may have compressing elements 142.It was found that in some cases end portions of the heat shrinkcomponent 100 have a remarkably higher dissipation of heat than thecenter portions of the heat shrink component 100. End portions are theareas between 1 and 50 mm from the end, in most cases around 30 mm.

As shown in FIG. 31, a heating unit 120 may be arranged in a part oralong a complete length of a heat shrink component 100, shown in FIG. 1.The heating unit 120 comprises an electrically conductive lead 106 thatis arranged in a meandering fashion so that a main part of theelectrically conductive lead 106 extends along a longitudinal axis 110.When the heat shrink process is performed, the meander loops of theelectrically conductive lead 106 move closer together.

In an embodiment shown in FIG. 32, the heating system comprises only oneheating unit 120. In order to form a first heating zone 158 and twosecond heating zones 160, the electrically conductive lead 106 isarranged in the first heating zone 158 to form tight undulations 162 inorder to cover a larger area on the heat shrink layer 108 than in thesecond zones 160. In the shown embodiment, the second heating zone 160is arranged between a peripheral end of the heat shrink component 100and the first heating zone 158.

Due to the undulations 162, more heating energy and thus in many cases ahigher temperature is generated in the first heating zone 158 comparedto the second zones 160 when the electrically conductive lead 106 isenergized by applying an electrical current through it. Consequently,the heat shrink process starts in the first heating zone 158 and thenadvances along the longitudinal axis 110 towards the second heatingzones 160 and to the peripheral ends of the heat shrink component 100.As schematically indicated in FIG. 32, there is a smooth transition inthe density of the undulations 162 from the central first heating zone158 towards the straight arrangement at the end of the second heatingzones 160. This geometry allows for a gradual temperature profile alongthe longitudinal axis 110 at least at the beginning of the heatingprocess.

In various embodiments, any suitable form of the undulations 162 may bechosen in order to cover a larger area with the electrically conductivelead 106 in the first heating zone 158. For instance a zigzag structuremay also be used. It is also clear that a distinct geometricaldefinition of the ends of the zones 160 and 158 cannot be made, anysuitably shape can be used according to the present invention.

In an embodiment shown in FIG. 33, the electrically conductive lead 106has a different material, and a different specific resistance, and/or areduced cross-section in the first heating zone 158. This arrangementalso leads to a higher temperature in the first heating zone 158 whenthe electrically conductive lead 106 is energized by applying anelectrical current through it. Consequently, the heat shrink processstarts in the first heating zone 158 and then advances in two directionsalong the longitudinal axis 110 towards the second heating zones 160 andto the peripheral end of the heat shrink component 100.

In another embodiment shown in FIG. 34, a structured conductive trace(also called film) 116 is used as the electrically conductive lead. Forinstance by etching or a photolithographic technique the electricallyconductive film 116 is formed to have smaller cross-sectional dimensionsin the first heating zone 158 compared to the dimensions it has in thesecond heating zones 160. When the electrically conductive film 116 isenergized by applying an electrical current, the resistance is higher inthe first heating zone 158 compared to the resistance in the secondheating zone 160. Consequently, the heat shrink process starts in thefirst heating zone 158 and then advances in two directions along thelongitudinal axis 110 towards the second heating zones 160 and to theperipheral end of the heat shrink component 100.

In another embodiment shown in FIG. 35, the heating unit 120 has anelectrically conductive lead 106 which is formed by a wire. The wire inthis embodiment is laid as a single wire in the first heating zone 158and splits into two branches 164 and 166 which are electricallyconnected in parallel. Consequently, an electrical current I that isflowing through the electrically conductive lead in the first heatingzone 158 is divided into two smaller currents I1 and I2 in the first andsecond branches 164, 166 with I=I1+I2. The smaller currents I1 and I2cause a lower temperature in the second heating zones 160. Consequently,the heat shrink process starts in the first heating zone 158 and thenadvances in two directions along the longitudinal axis 110 towards thesecond heating zones 160 and to the peripheral end of the heat shrinkcomponent 100.

In other embodiments, more than two wires may be connected in parallelin the second heating zones 160 and that also in the first heating zone158 more than one wire can be present being connected in parallel, aslong as the current flowing through the wires arranged in the secondheating zones 160 is lower than the current flowing through the wires inthe first heating zone 158. It is also clear that the cross-sectionand/or the material of the wires 106 in the first heating zone 158 andthe second heating zones 160, meaning in the first and second branches164, 162 may not be identical. The electrically conductive lead 106 mayhave a different cross-section, such as a different cross-sectionalarea, in the first heating zone 158 than in the second heating zone 160.In another embodiment, the electrically conductive lead 106 may have adifferent specific conductivity in the first heating zone 158 than inthe second heating zone 160.

In another embodiment shown in FIGS. 36-38, the heating unit 120 issmaller than in the embodiments shown in FIGS. 32-35. Consequently, theheating unit 120 only covers a limited region of a heat shrink component100. The heating unit 120 may either comprise a wire forming theelectrically conductive lead 106 (see FIG. 36) or a printed or etchedmetal film 116 as shown in FIG. 37. Each heating unit 120 has terminals168 to connect a power source.

As shown in FIG. 38, a heat shrink component 100 may be covered by threeheating units 120 which are arranged along the longitudinal axis 110.Each of the heating units 120 may be formed as shown in FIG. 36 or 37.The three heating units 120 are controllable independently from eachother to be provided with an electrical current via their terminals 168,so that three heating zones as indicated by the encircled numbers 1-3are formed. For instance, the center zone may be a first heating zone158 which is energized before the second heating zones 160, so that ahigher temperature is reached first in the first heating zone 158 andlater in the second heating zones 160. Again, the heat shrink processstarts in the first heating zone 158 and then advances in two directionsalong the longitudinal axis 110 towards the second heating zones 160 andto the peripheral end of the heat shrink component 100.

In other embodiments, these three heating units 120 may also becontrolled differently, so that for instance one of the peripheralheating units is energized first, the others following sequentiallyalong the longitudinal axis 110. Any suitable temperature profile may bechosen for achieving a heat shrink process that avoids the inclusion ofair and leads to a uniform and high performance heat shrink product. Forinstance, in order to speed up the heating process, the heating unitswith the encircled numbers 1 and 3 may be started to be energized at thesame time as the one with the encircled number 2, but with a lowercurrent. This scheme leads to a pre-heating effect which allows a fastershrinking later when the pre-heating heating units are fully energized.

In another embodiment, as shown in FIG. 39, two or more heating units120 according to FIG. 36 or 37 may also be arranged on a heat shrinklayer 108 in a way that an overlapping area 170 is created. Thisoverlapping area 170 has a higher density of heating wires and thereforeforms a first heating zone 158 which reaches a higher temperatureearlier than the second heating zones 160. Consequently, also with thisembodiment the heat shrink process starts in the first heating zone 158and then advances in two directions along the longitudinal axis 110towards the second heating zones 160 and to the peripheral end of theheat shrink component 100. The width of the first heating zone 158 maybe larger than the overlap 170, depending also on the material andthickness of the heat shrink product.

A similar effect can also be achieved by using two traces of wire 106 onone heating unit 120, as shown in FIG. 40. In the first heating zone 158the heating wire is laid with a higher density compared to the secondheating zones 160. Consequently, a higher temperature is reached earlierin the first heating zone 158 compared to the second heating zones 160.In this embodiment the heat shrink process starts in the first heatingzone 158 and then advances in two directions along the longitudinal axis110 towards the second heating zones 160 and to the peripheral end ofthe heat shrink component 100. The electrically conductive leads 106 arearranged to form two independent electric circuits 172, 174 arranged onone carrier film. The first electric circuit 172 is advantageouslyelectrically insulated from the second electric circuit 174.

A heat shrink component 100 according to another embodiment is shown inFIG. 41. According to this embodiment, the heat shrink layer 108 is indirect contact with the heating unit 120 only in the first heating zone158. In the second heating zones 160, one or more thermal insulationlayers 176 are arranged between the heating unit 120 and the heat shrinklayer 108. This geometry leads to a delayed heat input to the heatshrink layer 108 in the second heating zones 160, compared to the firstheating zone 158. Consequently, also with this embodiment the heatshrink process starts in the first heating zone 158 and then advances intwo directions along the longitudinal axis 110 towards the secondheating zones 160 and to the peripheral end of the heat shrink component100.

As shown in FIG. 41, more than one thermal insulation layers 176 may bearranged with a mainly constant thickness in order to achieve a gradualtemperature profile along the longitudinal axis 110. The thickness ofthe thermally insulating layer 176 may change continuously and/or thethermally insulating properties may change along the axis 110, while forinstance having the same layer thickness.

In another embodiment shown in FIG. 42, one or more thermally insulatinglayers 176 may also be arranged to encompass the heating unit 120 andthe heat shrink layer 108. The heating unit 120 is therefore arrangedcloser to the heat shrink layer 108 than the thermal insulation layer176. In this configuration, the thermal insulation has the effect thatin the first heating zone 158 a more efficient heating is achieved byredirecting the heat towards the heat shrink layer 108. Consequently ahigher temperature is achieved earlier in the first heating zone 158compared to the second heating zones 160. As shown in FIG. 42, more thanone thermal insulating layers 176 are provided to achieve a changingthickness in order to generate a gradual temperature profile along thelongitudinal axis 110. Of course, any suitable number, shape, andthermal properties of the thermally insulating layers 176 may beprovided in various embodiments.

In another embodiment shown in FIG. 43, the thermal insulating layer 176is a single layer with a thickness that changes over the axial directionand has its highest value in the first heating zone 158, graduallydiminishing its thickness in the second heating zones 160. The thermalinsulation layer 176 covers the entire heat shrink product 100 as anadditional protective layer and optionally may further have an extension178 that closes the arrangement during the heat shrink process at leastpartly against the environment.

In the embodiment shown in FIG. 43, the thermal insulation 176 has theeffect that in the first heating zone 158 a more efficient heating isachieved by redirecting the heat towards the heat shrink layer 108.Consequently a higher temperature is achieved in the first heating zone158 compared to the second heating zones 160. A gradual temperatureprofile along the longitudinal axis 110 is achieved. With regards toFIG. 43 it becomes again apparent that a sharp distinction between thefirst and second heating zones 158, 160 cannot be made. It also has tobe mentioned that in the ideal case there are no two zones rather thanan area 158 where to start, which e.g. covers parts of the central areaof a cable joint where the connector and the Faraday cage of the heatshrink layer 108 are sitting, and which then continuously advancestowards the ends.

The embodiments of the present invention are capable of shrinking widelyused energy products, like LV, MV, and even HV joint bodies,terminations, sleeves (such as rejacketing sleeves), and molded parts(such as break out boots and caps) without using an open flame andinstead using electrical energy. Because the application typically is afield installation, the power source beneficially uses batteries, eitheravailable in the van of the cable jointer staff or to be carried to theplace of installation. Alternatively, a generator, either available inthe van or transportable over limited distances, can be used. For safetyreasons, the voltage can be limited to values in the magnitude of 20 V,at maximum 24 V. In order to be compatible with installation times thatare reached using open flames, the shrink times of a typical MV jointbody should not exceed a maximum of 10 minutes.

In order to achieve short shrink times, heating wires 106 and films 116may have temperatures as high as possible, preferably above thedestruction temperatures of the heat shrink products. The heat spreadinglayer 124 spreads heat energy to be transferred into the heat shrinkcomponent 108, ensuring that the heat transfer ideally happens all overthe entire surface area. The heat spreading layer 124 acts as thermalinsulation against the environment and to create an additional heatcapacity, which both improve the overall quality and reliability of theheat shrink process.

In order to achieve a gradual shrinkage, the heat transfer may becontrolled to be uneven over the length of the heat shrink product.Layers with a relatively low coefficient of thermal conduction due tothe material and/or their construction (for instance their surface,overall shape, and/or included air cavities) may be arranged radiallyinwardly and/or radially outwardly relative to the heating conductors. Adifferent external or internal thermal insulation was also foundimportant to speed the shrinkage in general and may be chosen to differover the length of the heat shrink product to enable or support agradual shrinkage behavior. Sensors may additionally be used to allowthe control system to drive the gradual shrink process, for instance byproviding different power over time. In another embodiment, theresistance of one metal conductor may be changed along its length andthus over the length of the heat shrink product; this can be done bychanging the cross-section and/or the material.

The present invention can be employed with the following exemplaryspecific dimensions and characteristics.

Although any kind of heating wires 106 can be used, the conductivity ofthe wires 106, in an embodiment, is at least 1·10⁷ S/m. The power sourceprovides a voltage that is a DC voltage below 60 V or an AC voltage of25 V RMS.

A cross-sectional area of the heating conductor 106 is between 0.007 mm²and 0.8 mm², equaling to wires 106 of 0.1 to 1.0 mm diameter. Conductivefilms 116 must have according dimensions, typically these films havethicknesses in the range of 5 μm to 25 μm. The temperature of theconductor during the heating is at least 120° C., max. 450° C., for aheating time of 20 minutes or less. The value of 120° C. is a typicalshrink temperature for heat shrink products. There are variants thatshrink at 110° C. and a very special material which is not used onenergy products starts to shrink at 65° C. Given temperature losses tothe environment, the temperature of the conductors must be far above120° C.

A typical MV joint body has a wall thickness of 3.5 mm of the heatshrink layer (plus elastomeric layer), a length of 420 mm and an outerdiameter of 68 mm (surface area is 9 dm²). In successful trials sixheating units 120 with 3.3 meter of wire each (diameter 0.22 mm) wereused. With a power source providing 24 V, these six heating units 120were connected in parallel and heated up to 200° C. to 350° C.temperature of the wires 106. The shrink time was 10 min, using thermalinsulation and heat spreading.

If the wire 106 diameters are chosen smaller, then each heating unit 120must have less meters of wire 106. Accordingly, more than six heatingunits 120 are to be configured to allow a 24 V power source to heat upthe heat shrink component to the required temperatures. In anembodiment, a circumferential distance between heating wires 106 may bebelow 50 mm, such as below 20 mm, in the non-recovered condition,reducing any issues with distributing the heating energy.

If another heat shrink product has less surface area, then a lowernumber of heating units 120 (thus less meters of wire) are needed.

If another heat shrink product has a lower wall thickness, then acomparably lower number of heating systems and less meters of wire areneeded. The dependency on the wall thickness does not seem linear. Itappears that even a stack of multiple heat shrink sleeves resulting in10 mm total wall thickness can be heated with about the same settings asthe typical MV joint body having a wall thickness of 3.5 mm. There is,of course, a dependency on the overall shrink behavior of the particularheat shrink material. By adapting the composition of the heat shrinkmaterial, the shrink temperature and the ease of shrinking can bevaried.

What is claimed is:
 1. A heating system for heating a heat shrink layerof a heat shrink component during a heat shrink process, comprising: aheating unit arranged in thermal contact with at least a part of theheat shrink layer and heating the heat shrink layer to a heat shrinktemperature, the heating unit has a first heating zone and a secondheating zone, the first heating zone has a different heating energy thanthe second heating zone for a period of time of the heat shrink process.2. The heating system of claim 1, wherein the heating unit includes afirst heating unit arranged in the first heating zone and a secondheating unit arranged in the second heating zone, the first heating unitand the second heating unit are controllable to be heated differently.3. The heating system of claim 1, wherein the heating unit includes afirst heating unit and a second heating unit arranged to be overlappingin an overlapping region, the overlapping region forms the first heatingzone and a non-overlapping region forms the second heating zone.
 4. Theheating system of claim 1, wherein the heating unit has an electricallyconductive lead heated by an electrical current flowing through theelectrically conductive lead.
 5. The heating system of claim 4, whereinthe electrically conductive lead covers a larger area in the firstheating zone than in the second heating zone.
 6. The heating system ofclaim 4, wherein the electrically conductive lead has a differentcross-section in the first heating zone than in the second heating zone.7. The heating system of claim 4, wherein the electrically conductivelead has a different specific conductivity in the first heating zonethan in the second heating zone.
 8. The heating system of claim 1,further comprising a thermal insulation layer arranged in the firstheating zone and/or in the second heating zone.
 9. The heating system ofclaim 8, wherein the thermal insulation layer is arranged between theheat shrink layer and the heating unit in the second heating zone. 10.The heating system of claim 8, wherein the thermal insulation layerencompasses the heat shrink layer and the heating unit in the firstheating zone.
 11. The heating system of claim 4, wherein theelectrically conductive lead is a metal wire having a cross-section witha round, oval, or polygonal shape.
 12. The heating system of claim 4,wherein the electrically conductive lead is an electrically conductivefilm.
 13. A heat shrink component, comprising: a heat shrink layer; anda heating system including a heating unit arranged in thermal contactwith at least a part of the heat shrink layer and heating the heatshrink layer to a heat shrink temperature, the heat shrink componenthaving a first dimension in an expanded state and a second dimension ina shrunk state after heating, the first dimension is larger than thesecond dimension, the heating unit has a first heating zone and a secondheating zone, the first heating zone has a different heating energy thanthe second heating zone for a period of time during the heating.
 14. Theheat shrink component of claim 13, wherein the second heating zone isarranged between a peripheral end of the heat shrink component and thefirst heating zone.
 15. The heat shrink component of claim 14, whereinthe first heating zone has a higher heating energy than the secondheating zone during the period of time.
 16. The heat shrink component ofclaim 13, wherein the heat shrink layer has an essentially tube shapedform with a longitudinal axis.
 17. The heat shrink component of claim16, wherein the heating unit radially encompasses the heat shrink layerwith the first heating zone and the second heating zone spaced apartalong the longitudinal axis.
 18. The heat shrink component of claim 13,wherein the heating unit has an electrically conductive lead heated byan electrical current flowing through the electrically conductive leadand a heat spreading layer in thermal contact with the electricallyconductive lead, the heat spreading layer circumferentially distributinga heat generated by the electrically conductive lead.
 19. The heatshrink component of claim 14, further comprising a compressing element,the electrically conductive lead arranged between the compressingelement and the heat shrink layer, the compressing element pressing theelectrically conductive lead toward the heat shrink layer during heatingof the heat shrink layer.
 20. A method of assembling a heat shrinkcomponent, comprising: providing a heat shrink component in an expandedstate, the heat shrink component including a heat shrink layer and aheating system including a heating unit in thermal contact with at leasta part of the heat shrink layer; connecting an electrical power sourceto the heating unit; and heating the heat shrink layer to a heat shrinktemperature with the heating unit, the heat shrink component shrinkingfrom a first dimension in the expanded state to a second dimension in ashrunk state, the first dimension is larger than the second dimension,the heating system has a first heating zone and a second heating zone,the first heating zone has a different heating energy than the secondheating zone for a period of time during the heating.